Electrostatic acoustic amplifying device



June 23, 1931. I c. OJTAYLER ELECTROSTATIC ACOUSTIC AMPLIF YING DEVICE Filed April 9. 1950 c. 0. Jhyler [nwntar 3 4. Attorney Patented June 23, 1931 CLIVE OSBORNE TAYLER, OF VICTORIA, BRITISH COLUMBIA, CANADA ELECTROSTATIC ACOUSTIC AMPLIFYIN G DEVICE Application filed April 9, 1930. Serial No. 442,907.

' This invention relates to electrostatic loud speakers, for radios, phonographic recordings for theatres, and other like acoustic amplification purposes.

Its object is the production of devices of this character which are both simpler and of 'IIIOI'G robust construction and therefore have less liability to derangement than those of the type hitherto constructed, the parts of which are frequently so delicate both in form and substance as to give rise to defects and difliculties when least expected and which aretraceable to'these peculiarities of structure.

With some apparatus of this type it has been necessary to use a metal baseplate of cellular formation, where the plate member consists of numerous small apertures in regular'and spaced apart relation, and so proportioned that the intervening space separating adjacent apertures is relatively narrow and consequently weak. 7

In other apparatus the baseplate has somewhat the same general character but the in- 26 dividual cells take the form of receptacles which have punctured incisions, and t0 the effect of which certain objections may in my opinion be taken. p

Q My invention aims to eliminate this in- 30 herent weakness ofthe base member, and to impart to the apparatus as a whole a more definite mechanical structure which lends itself to mass production methods, besides having more inherent efliciency with direct 85 adaptability to adjustment for acoustic reasons. My device has three essential elements.

A'substantial metallic baseplate having a series of relatively narrow slits in parallelism. An insulating member comprising a sheet of thin hard rubber or other like effective insulator, this sheet being effectively cemented to the surface of the base member and itself providing the resonant cavities of the de- 145 vice. These latter consist of clean edged apertures at spaced apart intervals which provide an intervening strip of insulation of the order of half the width of the aperture. This seried arrangement of apertures covers the entire effective area of the sheet. It will thus be seen that these apertures in combination with adj acent members-each of which is effectively cemented to one surface of the insulating sheet-form'shallow cavities held in comparative rigidity, each of which becomes a resonant unit of the device. It should here be noted that each of these cavities obtains an atmospheric outlet through one of the aforesaid slits in the base member, which slit crosses the cavity substantially at its centre, a and provides by the adjustment of its width a delicate and effective means for readily varying the resonant qualities of the cavity according to requirements. This feature .1 regard as highly important and it may be (15 classed as a salient point in the device.

The third element consists of a sheet of metal leaf, such as tin foil or its equivalent, and having an effective area equal to that of each of the other members. This third element may probably with advantage be coated with a film of line insulating varnish on the surface which opposes the cellular insulating sheet before the two surfaces are finally cemented together.

The operative area of each of the three members is the same, and the inner surface of each of the metallic members is preferably coated with a thin film of high grade insulating varnish before the three members are ce- 8O mented firmly together. This insulating film is a necessary precaution against the possibility of sparking between the members, due to the comparatively high voltage employed.

When the members are thus compacted together a comparatively rigid compound struc ture is produced, and the base member being of relatively substantial form may readily be provided with means for uniting adjacent units in multiple, so that they may be connected to obtain any desired value of soundv amplification. Should it be deemed necessary to introduce a. slight tensional strain upon the vibrating member, means for pro.- viding this to the utmost degree of refinement are available by cambering the surface in two directions one right angular to the otherand providing means for measuring and regulating the camber as desired.

However as the tensioning of the foil induces a higher frequency the ready means of obtaining it is only indicated as a remote. possibility, as it would not. be required to any appreciable eXtentthe frequency calibra tion of my device being obtained by a modification of the-width'of the slits in-the base member.

The invention is more clearly 'd'escribedby the aid of the drawings accompanying and forming a part of this application, and in which i i Fig. l is a surface view of one unit ofmy device, showing portions of the two members broken away so as to expose the member underneath.

Fig. 2 is an end viewe1;aggeraiied to diagrammatic form so as to show the relative positions of the various members, and

Fig. 3 is a fragmentary view of the base member to an enlarged scale. a

In these drawings the numeral-5 indicates the inner surface of the metallic base member, 6 arenarrow incisions or slits therein, 7 is one of the rightangularly turnededges-which are available for securing adjacent'units on any one or more of the. four the broken edge of the part shown. The cellular insulating member is shown at 9; and in the example indicated is of the natureof hard rubber with clean edged apertures of rectangular form 10. The members 5*,and9 are so positioned thatthe narrow incisions 6 are transverse and central of the apertures 10 in the respective members, the sound'waves from the cavities formed or bounded by the rectangles 10 find egress through the incisions V 6 and these are'available for'calibrat-ionvpur poses by slightly altering their width. and.

thuseifecting a corresponding alteration in the frequency of the vibrating-member. This latter is indicated at lland consists of a sheet corresponding in size with. that of the two other members 5 and 9 but of metal foil such as tin foil or its equivalent in some form of m etallized film, 'lh-e inner surface-of this foil is preferably'coated' with a: thin film of high grade insulating varnish, the inner surface of the base member 5' being similarly treated, and the. three memberseffectively cemented together.

In operation, suitable terminalsare afliXed to the two metallic'members, and the base member 5 is provided with a positive bias charge varying between the limits of 200 to 500volts, the instrument being connected in sides, '8 indicates the usual way and arranged with the base member inwards.

The unit or any number of them may thus be readily mounted in suitable framework, and may form the panel of a cabinet or on a wall of an auditorium.

Having now fully described the nature of my said invention, what I claim and desire to secure by Letters Patent, is:

' 1. In an electric static acoustic amplifying device the combination comprising, a base member consisting of a sheet of. metal rectangular in form. and having'a seriesof parallel lines of narrow slots formed therein, said slots being-in spaced apart relation in said lines and positioned" transversely of said sheet, said member being coated with insulate ing varnish on its operative edges and surface, a sheet. of, insulating fabric of corresponding rectangular form and size and having, a series-0f clean edged-rectangular apertures in spaced ap art-relationand positioned; side by sideanda'endtowards rend: andin such spaced relation that thewidth ofinsu lation between adj acent. apentureszis less than half the-width of theisaid aperture=, the relative. positions of'the two=said;sheet. members being: such that the narrow slots-in the one. span. the apertures-inthe other at a pointintermediate of their ends, athird sheet meme. ber corresponding informand: size: with the other said membersv and comprising ia: film of: super-thin metal, said. metal filmahavinga coating of insulating varnish on one surface, the varnished surfaces of the two; metallic 100 members aforesaid: beingfirmly cemented to the respective surfaces of the saidinsul'ati'ng member, whereby, when an electric: wave: im-- pulse of suitablefrequency is passed through the; two said metallic members-a soundi Vi: 10 bration w il-lbeset up by thezsaiidr super-thin member within the said'aperturesand emitted through the said, narrow slots: in addition to the-sound propagated by the outwardif-ace of the vibrating member 1-10 2. In an electrostatic acoustic amplifying device the combinationlcomprisingthree sheet members of substantially similar contour-and surface area, the said three members being arrangedinseriessurface to surface the inner one of the-said members-being of high grade insulating fabric and havinga'series of cleanedged apertures in closely spaced relation occupying the entire operative area 'of'the' said sheet members, onezof the outer of. the saidthree members being adapted to form the base member'ofthedevice-andbeing of sheet metal and hav-ing a series ofnarrow incisions so positioned that when the last said member isin operative position-withregard to the said insulating memberthe-apertures in the latter are traversed-by someportion of the said narrow incisions in-thebase member, the other outer member; of? the :three saidmembers being- -of super thinrmet'al the three said members being eflectively cemented together, whereby the cavities formed by the apertures in the said insulating member in combination with the two other said members become resonant under the vibration set up by the said super-thin member when an electric wave impulse of suitable frequency is passed through the two said metallic 7 members. I o 10 In testimony whereof I have hereunto aflixed my signature.

OLIVE OSBORNE TAYLER. 

